The Diabetes Prevention Program (DPP), a NIH funded, multi-center trial focusing on the primary prevention of Type II diabetes, was initiated in 1994. A unique aspect of the DPP screening process is that a large number of individuals with early Type II diabetes, characterized by isolated postprandial hyperglycemia, will be identified. By virtue of already having diabetes, they will not be candidates for the DPP. This gives rise to the unique opportunity to study these rarely identified individuals with early diabetes, and explore possible mechanisms by which their risk for disease progression and development of complications may be reduced. In collaboration with Washington University in St Louis, we are proposing a pharmacological intervention to study prospectively the natural history of the early stages of Type II Diabetes. The overriding hypothesis of this proposal is that isolated postprandial hyperglycemia plays a significant role in the progression from early post-prandial diabetes to overt Type II diabetes. Intervention with the alpha-glucosidase inhibitor, acarbose, will selectively ameliorate post-prandial hyperglycemia by delaying carbohydrate digestion. This study will describe the time course changes in overall glycemic control, insulin secretion and clearance, insulin sensitivity and body composition. In addition, important information regarding the progression of macrovascular and microvascular complications will be obtained. Upon completion of these protocols, the common features of the study population across sites will allow for the unique opportunity to share data sets and compare treatment approaches that potentially will have significant impact on one of this country's most serious public health problems.